Determination of the rate of growth of the livers of living donors and recipients. The unique ability of the liver to regenerate to a predetermined size after resection or transplantation makes partial liver transplants possible. Much of what is known about hepatic regeneration is still poorly understood. A better understanding of the process will facilitate partial liver transplantation in many ways and bring it under some degree of external control. Regeneration and recovery can be hastened. Study objectives include: 1. Determination of the regeneration process following donation of a lobe or segment of liver. 2. To study the duration of regeneration process in the recipient following transplantations of partial livers. 3. To determine the effects of factors unique to transplantation on hepatic regeneration by comparison of the process in donors and recipients. 4. To study the relationship between the total mass resected or transplanted and the duration of regeneration process. 5. To determine if there is any reliable correlation between commonly measured serum proteins and the degree of hepatic regeneration. 6. To establish parameters for specific assessment of the function and adequacy of partial grafts during the period of regeneration. 7. To explore the possibility of manipulating the regenerative process to reduce the mass of liver necessary for a successful partial transplant and hasten post operative recovery. The study will involve approximately donors and recipients. All research will be carried out at the General Clinical Research Center. Participants will undergo standard evaluation which will be used for baseline information for the study. Subjects will have Magnetic Resonance Imaging (MRI) or Computed Tomography Scan (CT) several times after surgery to determine the rate of regrowth of donor liver and transplanted liver. Blood tests will also be done at these times to establish normal laboratory values.